The analysis of dissolved or dispersed chemicals in water can be implemented with the assistance of gas-chromatographic vapor space analysis. In this method, the specimen is brought into a gas-liquid distribution equilibrium with a carrier gas in a vapor space. After reaching equilibrium, the specimen is withdrawn from the vapor space and gas-chromatographically analyzed. In such known extraction techniques, the vaporized liquid in the vapor space is replaced with a carrier gas after taking the specimen. Introduction of the carrier gas disturbs the equilibrium that had previously been established. Equilibrium is subsequently re-established, and a second specimen is taken. This procedure is repeated several times in order to determine the respective concentration values of the gaseous specimens. The quantity of substances contained in the specimen can be derived from the relationships between the identified concentration values. This technique provides relatively precise measurements for substances having a high fugacity.
In order to ensure the accuracy of such known methods, the gas-liquid distribution equilibrium must be attained, or "set", as quickly as possible. Short setting times are achieved when the contact surface between the liquid and the carrier gas is extremely large. In one known method, the contact surface is kept as large as possible by continuously bubbling a gas stream through the liquid. Such a method is also known from the article "Feldmessung von Emission und Deposition Atmosphaerischer Spurengase im Boden und Wasser", Spurengasanalytik Suppl. 3/85, pages 74-78, and from the article "Continuous Monitoring of Volatile Hydrocarbons in Water at the ppb Level", International Laboratory, September 1989, pages 16-20. The gas bubbles or gas effervescence introduced into the liquid can present a large contact surface to the liquid, provided that the diameter of the individual bubbles can be kept small and that there are a large number of such small-diameter bubbles. When rising in the liquid, the volatile constituents are collected in the gas bubbles. The specimens that are taken are usually pre-concentrated in a collector arrangement, desorbed, and then ultimately supplied for further analysis.
Extraction with gas bubbles can be continuously or discontinuously implemented. However, known methods are limited to liquid specimens that contain no tensides or frothing agents that tend to cause the liquid to foam. When foam enters into the vapor space, the entire extraction apparatus becomes unusable. A considerable portion of industrial waste waters contains such surface-active compounds. These types of contaminated liquid can not be treated with the known method and apparatus. The known method is also unsuitable for analyzing slurries, since the particles dispersed therein are potentially difficult to absorb into the gas bubbles. The contact between the various parts of the slurry and the gas bubbles that rise freely and slowly (according to the Archimedean principle) can be deficient for purely mechanical reasons. An increase in the gas pressure cannot compensate for such deficiencies; on the contrary, increased pressure causes the small gas bubbles to fuse together; thus forming larger gas bubbles. The larger bubbles rise slowly, and reduce the overall contact surface of the gas, thus further reducing the transfer rate of the substances to be removed for analysis.